Paul's arrest and transfer to Rome apparently prevented him from gathering his possessions.
the cloak: Winter was approaching (4:21).
Carpus might have hosted Paul in Troas. Mentioning Troas suggests Timothy was still in Ephesus and would travel through Troas, a port town.
my scrolls, especially the parchments: These writings may have included Scriptures, personal notes, letters to Paul, copies of Paul's own letters, and other Christian and Jewish materials.